This invention relates to impact printers and, more particularly, to impact printers wherein a ribbon moves between a ribbon storage area and a print point to continuously supply fresh ribbon to a position between a character element and a print receiving medium.
In printers of this type including typewriters, the ribbon storage has been provided by a cartridge. These cartridges are removable so as to permit the ribbon supply to be replenished by merely replacing the ribbon cartridge.
In various printers including typewriters such as those manufactured by IBM and SCM, the platen which supports the print receiving medium in the impact printing position remains stationary and the character printing elements move along the platen to the various printing positions. In these printers the cartridge has been mounted for movement with the character elements and the print point so as to continuously supply fresh ribbon to the print point as the character elements advance. Typically, the cartridge has been supported on a carriage which moves linearly along the platen where the character elements may be mounted on a ball or wheel oftentimes referred to as a daisy. Where the printer is to operate at high speeds as in the case of a typewriter operating in an automatic memory mode, the carriage must be capable of very high acceleration and deceleration rates which places a substantial demand on the motors, drivers and power supplies for the carriage. Where the carriage also accelerates and decelerates the ribbon cartridge which is mounted on the cartridge, the demands on the carriage motor, driver and power supply can become very substantial.
In order to minimize these demands, ribbon cartridges which are mounted on the cartridge have had a limited ribbon capacity. Although this has achieved the objective of limiting the weight which must be accelerated and decelerated as the carriage and the print point move, there have been certain, significant penalties. First, the cartridge must be changed more frequently where the ribbon capacity is small. This is of course time-consuming for the operator of the printer or typewriter and also presents some risk that the print receiving medium may be in some way defaced by removing and replacing the cartridge, e.g., smearing is not at all uncommon in such circumstances. Second, the smaller ribbon cartridges include a rather complex mechanism which is quite costly when one considers that the cartridge is in effect disposable. Where the ribbon capacity is quite limited, the cost of the mechanism relative to the ribbon of the cartridge becomes quite substantial and the overall cost of the cartridge per strike becomes high.
As described in copending application Ser. No. 833,270 filed Sept. 14, 1977 in the name of Dan W. Matthais, assigned to the assignee of this invention, these difficulties of the prior art have been overcome by providing a laterally movable character printing means such as a print which is juxtaposed to a support means such as a platen or a print receiving medium such as paper in combination with a stationary storage means for a ribbon carrying a printing medium where the ribbon is advanced past the movable print point in printing relationship with the print receiving medium while maintaining a substantially constant ribbon path length from the stationary ribbon storage means to the movable print point.
In a preferred embodiment of the aforesaid invention, the substantially constant ribbon path length is achieved by means of a first flexible leader which extends from the ribbon storage means to the print point and a second flexible leader which extends from the print point to the storage means. The ribbon is supported by and moves along these flexible leaders.
However, such flexible leaders tend to disturb the printing medium, i.e., the ink, of the ribbon as the ribbon moves therethrough. This is particularly true where the flexible leaders assume compound or reverse curvature so that the side of the ribbon bearing the ink or printing medium necessarily rubs against the flexible leader when the tension is applied to the ribbon and a portion of the surface of the ribbon carrying the ink contacts the surface of the leader due to the compound or reverse curvature. Where the printing medium or ink is of the correctible or lift-off type, the ink may be easily disturbed so as to impair the printing operation. Furthermore, the flexible leaders may be unruly and produce irregular curvatures which interfere with the operation of the printer components.